Update git submodules

* Update docs/submodules/yardstick from branch 'stable/danube'
  - add release date

    Change-Id: Icf12b7a59144754f65f67ed54a5c455a64c5042f
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index d553d66..795438d 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit d553d668cfcb24befeeb3464b6d0b5d328c45a2d
+Subproject commit 795438d0766a0c1bd7480c68f3234434019e6917